1 . Field of the Invention
The present invention relates to an audio signal processing technique.
2 . Description of the Related Art
In some cases, with an audio apparatus, after an analog audio signal is temporarily converted into a digital audio signal by means of an A/D converter, the digital signal thus converted is subjected to volume adjustment or frequency characteristics modulation (equalizing) by means of digital signal processing, and the digital signal thus processed is again converted into an analog audio signal by means of a D/A converter.
FIG. 1 is a block diagram which shows a configuration of an audio apparatus investigated by the present inventor. An audio apparatus 1r includes a sound source 2, an electroacoustic conversion element such as a speaker or a headphone (which will collectively be referred to simply as the “speaker” hereafter) 4, a first audio signal processing circuit 200r, and a second audio signal processing circuit 100.
The sound source 2 is configured to output an audio signal S1. The sound source 2 is configured as a CD player, a DVD player, or a silicon audio player, having an analog output, for example. The first audio signal processing circuit 200r includes multiple input ports Pi1 through Pi3, each of which allows the audio signal S1 to be received from the sound source 2.
A selector 50 is configured to select the audio signal input to an input port selected by the user from among the input ports Pi. The A/D converter 54 is configured to convert the analog audio signal S2 received from the selector 50 into a digital audio signal S3.
The amplitude, i.e., the volume, of the input audio signal input to each input port, changes depending on the respective sound sources. Thus, a digital gain control circuit 70 is configured to multiply the digital audio signal S3 input to each input port by a gain (coefficient) set for the input port, in order to equalize the volume for each sound source. A second audio signal processing circuit 100, which is configured as a downstream circuit, is configured to perform various kinds of digital processing on the digital audio signal S4, and to convert the digital audio signal thus processed into an analog audio signal S5. The analog audio signal S5 is input to the speaker 4, which is downstream of the second audio signal processing circuit 100, via unshown amplifiers or filters.